The medium that allows for communication between an occult source and a prophet, spirit communication
Spirit communication and prophecy
The unknown communication medium might allow for a direct communication between a prophet and an occult source, some kind of broadcasting device in a far future. The communication might resemble hearing voices in your head. A prophet receiving such communication might not understand where these messages come from and this might create confusion or even a mystic feeling.
The way that a prophet enters the communication channel, making contact is also rather dubious. It seems that the communication takes place when the receiver concentrates, meditates or prays or in some case it takes place when he sleeps and dreams. If such communication media really exists and could be used, there will be great doubts on the reliability and credibility of results of any communication. Success might therefore depend on the credibility of the prophet.
If the medium realy could be used in this way, with whom would future scientists want to communicate with? How would they select a candidate?
A potential prophet must make clear in one way or another his willingness to communicate to the occult source before he could be chosen.
Since nobody knows the existence of such medium, or technology that might use it, nobody knows how to prepare for such a spirit communication. If people do prepare themselves for communication with spirit, ghost or an occult source than they do that with different and various motives and often religious intentions.
The kind of people that is interested in exploring this kind of communication might therefore not be the ideal group of people to participate in writing a correct confirmation of receipt for a time travel experiment. It might be very hard to find the right participant.
The resulting document is the receiver's interpretation of the message. A document written down by the prophet is all that is left over after the 'spirit communication' between him and the occult source. It is the presence of the document and the interpretation by its contemporaries that can cause consequences as well. Actions based on the presence of such a work could cause history to change in comparison with a history where such a document does not exist. These changes could be enormous.